1. Field of the Invention
The invention relates to apparatus for performing physical and/or chemical processes involving at least one liquid, and is particularly applicable to heat exchangers. In the apparatus, a liquid flows upwardly through parallel vertical tubes containing a mass of particles fluidised by the liquid. 2. Description of the Prior Art
An example of apparatus of this kind is described in U.S. Pat. No. 2,919,118. It is in principle possible to design and construct such apparatus so that a stable operational condition is maintained during operation. What is to be understood here by "a stable operational condition" is one in which the movement of the particles in the parallel tubes is substantially uniform, as between the different tubes. Nevertheless, it can happen that circulation of particles occurs within the assembly of tubes, for instance with careless operation and in particular if care is not taken when starting up the installation. Circulation of the particles is the state when in one or several tubes upward transport of the particles takes place, while in one or several other tubes, downward movement of the particles occurs. The path of circulation is closed by the top and bottom chambers.
If after careless starting, the fluidised particles in some tubes reach the top chamber before those in other tubes, particles originating from the former tubes will flow via the top chamber into adjacent tubes which are not yet quite filled with the fluidised particles. The result is a disturbance of the pressure balance among the tubes themselves, which causes circulation. If the apparatus is extensively used, this circulation of the particulate mass is undesirable. For example, if the apparatus is used as a heat exchanger, the efficiency of heat exchange decreases when circulation flows occur, because the temperature difference causing the heat transfer via the pipe walls is reduced. Consequently, a larger heated surface is required for the transfer of a given quantity of heat.